This invention relates to dental prosthetics, and more specifically to a dental prosthesis and a method for forming a dental prosthesis.
Damaged teeth are commonly restored using a crown or inlay. Similarly, missing teeth are commonly restored using a bridge. These crowns, inlays or bridges may be comprised of metal, ceramic, acrylic, composite or a combination of these materials. In addition, these crowns, inlays or bridges are typically formed using an investment, or xe2x80x9clost waxxe2x80x9d process.
The investment process begins with the formation of an impression of the pontic area, which has been prepared by a dentist to receive the crown, inlay or bridge. A model and die, which duplicate the shape of the patient""s teeth and gums, are then formed from this impression using a plaster type material. A pattern is then formed over this die, thus producing a likeness of the crown, inlay or bridge to be created. The pattern is generally made of an organic material, such as wax.
The pattern is invested in (i.e. coated with) a gypsum type material having a high dimensional stability and resistance to elevated temperatures. The pattern and gypsum investment are then subjected to temperatures sufficient to melt or vaporize the pattern so that the pattern material exits the gypsum structure, leaving a cavity inside the gypsum investment corresponding to the shape of the pattern. The cavity within the investment is then filled with the restorative material of choice, thus creating a reproduction of the pattern in the chosen material (metal, ceramic, acrylic, composite, etc.).
When a crown, inlay or bridge is to have a ceramic layer, a substructure is first constructed to reinforce and accept the ceramic layer. These substructures are generally comprised, in whole or in part, of metallic alloys. Problems have occurred in the use of such alloys due to the fact that the alloys generally contain trace elements that produce oxides on the surface of the alloys. These oxides are sometimes visible through the ceramic layer, making it difficult to produce ceramic restorations having a natural appearance. In addition, some of these oxides are known to have a toxic effect on the surrounding tissue. Although some techniques have been developed to address these problems by using a sintering process, these techniques are both costly and extremely sensitive to process parameters. Accordingly, there is a need for a dental prosthesis and a method of forming a dental prosthesis that is inexpensive and tolerant to variations in the process parameter.
An improved dental prosthesis has been developed comprising a metal alloy for use with the lost wax technique in conjunction with an infiltration process. This material may be used to produce inlays, crowns, bridges and substructures for ceramic restorations having significantly improved aesthetics and overall performance over previously known methods.
One group of embodiments of the present invention comprise dental prosthetic structures comprising a substructure comprising a casting alloy of a first precious metal and a second precious metal, and a coating that permeates the surface of the substructure, the coating comprising an infiltration alloy comprising the first precious metal.
The casting alloy is melted and cast into shape by a suitable method such as investment casting, and the infiltration alloy is then applied to the surface of the substructure and combined with the substructure through a heat treatment process. It is desirable that the cast alloy be both resistant to oxidation and compatible with the surrounding living tissue. In certain embodiments, gold is the major element of the cast alloy due to its characteristics of workability, resistance to oxidation and color, especially useful with ceramics.
In certain embodiments, the casting alloy is comprised of only two elements, gold and platinum. In certain embodiments,:the ratio of platinum to gold in the casting alloy is from 0 to 20% by volume. The percentage of each element is variable, and may be modified for different requirements as to the strength and melting temperature of the alloy for particular applications. The use of a higher ratio of platinum to gold has been shown to increase the strength of the alloy. In one embodiment, the melting temperature of the casting alloy is higher than both the melting point and the desired heat treatment temperature of the infiltration alloy. The casting alloy can be provided in ingot form and melted in the usual manner in the casting technique used by the technician after the restoration has been formed on the die in a manner well-known to one of skill in the art.
The infiltration alloy has similar properties to those described above for the casting alloy, particularly with respect to resistance to oxidation and compatibility with living tissue. In certain embodiments, the infiltration alloy may comprise up to 100% gold, although other embodiments may incorporate other elements; for example, the infiltration alloy may comprise up to 3% of silver to aid in the flow of the infiltration alloy. In certain embodiments, the infiltration alloy may be provided in a powdered form and may be mixed with a liquid carrier for ease of application.
The infiltration alloy is applied to the cast structure, placed in the furnace and brought up to the prescribed temperature so that it diffuses into the surface of the casting alloy. This process creates a layer of bright, oxidation-resistant alloy on the inner and outer surface of the cast structure without affecting the integrity or fit of the original casting. This technique lends itself to most standard techniques used in dentistry today, including but not limited to inlays, full crowns, bridges, ceramic restorations, broken stress bridges, precision attachments or any combination of the above.
In certain embodiments of the present invention, the infiltration alloy is comprised of gold particles which are adapted to diffuse into the cast alloy through a heat treatment process. In certain embodiments, the infiltration alloy thoroughly permeates the surface of the substructure alloy without changing the alloy""s integrity, leaving a thin coating of the infiltration alloy on the inner and outer surface of the substructure. A bonding agent may be used in certain embodiments to enhance the bonding of the ceramic layer to the treated substructure. Pure gold has been shown to be effective as a bonding agent. In certain embodiments, the surface of the substructure may be sandblasted with an abrasive such as aluminous oxide to improve adhesion. After creation of the substructure, an external ceramic layer can be created according to conventional techniques.
A second group of embodiments of the present invention comprise methods of forming a dental prosthesis comprising the steps of casting a substructure comprising a casting alloy of a first precious metal and a second precious metal; applying a coating to the surface of the substructure, the coating comprising an infiltration alloy of the first precious metal and a flowing element; and firing the substructure and coating at a temperature sufficient to cause the infiltration alloy to permeate the surface of the substructure.
A third group of embodiments of the present invention comprise methods of forming dental prostheses comprising the steps of: forming an alloy sheet comprising a first precious metal and a second precious metal around a die to form a substructure; soldering the substructure together at the edges; applying an infiltration alloy comprising the first precious metal to a surface of the substructure; and firing the substructure at a temperature sufficient to cause the infiltration alloy to permeate the surface of the substructure
The alloys and methods of the present invention are significantly improved over prior alloys and methods. Current practice in the field of the present invention does not incorporate an oxidation resistant, non-toxic alloy in the manner described in the present application. As the material is comprised of alloys of pure elements having a high degree of resistance to oxidation, there is essentially no oxidation of the metal. At the same time, this alloy has sufficient strength to allow construction of bridges. This invention provides a material and technique that is cost efficient and not unduly sensitive to process parameters.